EXPERIMENTAL INVESTIGATION OF CYCLIC PLASTICITY CONTINUUM DAMAGE EVOLUTION IN AN ENGINEERING COMPONENT SUBJECTED TO THERMAL LOADING

A thermal shock test facility is designed and built to enable a copper model slag tap component to be tested under cyclic thermal loading co nditions. Infra-red line heaters and pumped cooling water are used to impose temperature loading cycles on to the specimen. Accurate focussi ng of the line beaters using a two degree of freedom adjustment mechan ism, enables a heating area of width 3 mm to be applied to the specime n. Both the heating and the cooling processes are controlled by a prop ortional, integral, and derivative feedback micro-processor controller . Specimen temperature fields are obtained using thermocouples, and sp ecimen displacements and strains are measured using linear voltage dis placement transducers and strain gauges. A cyclic thermal loading test is carried out for approximately 7150 cycles on a model slag tap comp onent. The variations of specimen strains and displacements are record ed and compared with results obtained from a finite element viscoplast ic damage analysis. Good agreement between the predicted and experimen tal results is obtained. Microstructural examination of the specimen r eveals the development of persistent slip bands and micro-cracking at grain boundaries. This occurs at the regions of the specimen undergoin g cyclic plasticity due to the imposed cyclic thermal loading. The exp erimental observations of cyclic plasticity damage formation in copper undergoing cyclic thermal loading indicates the suitability of the Co ntinuum Damage Mechanics (CDM) theory to model the evolution of cyclic plasticity damage. The damage is characterized by the development of fields of micro-cracked grain boundaries due to the formation and inte raction of persistent slip bands within the grains.